"To limit damage from nematodes as well as waterborne fungi, bacteria, and viruses, hydroponic growers should use multiple sumps rather than a centralized system. Nematodes are easily spread within a greenhouse by any means of moving contaminated water, soil, or plant material. Nematodes are aquatic animals, so are especially easily moved in water. Recirculating hydroponic systems are especially vulnerable to nematodes and certain diseases because the entire system can become uniformly infested as soon as nematodes or disease organisms in or on roots anywhere in the system begin reproducing and get into the water. This can be a particularly serious problem because labeled chemical treatments are limited or nonexistent."

There are many thousands of species of nematodes, and not all of the are bad (pathogens) for the plants.